The present invention relates generally to a counterrotatable fan section and counterrotatable booster compressor for a gas turbine engine and, in particular, to a fan shaft assembly of a counterrotatable fan section which includes a compressor blade of the booster compressor integral therewith.
Gas turbine engines are continuously being improved so as to achieve greater thrust with lower noise and greater operating efficiency. One approach has become known as the bypass turbofan engine, where the airflow is divided into two separate and concentric flow streams. An outer flow stream (known herein as a bypass flow) is compressed only by a fan section of the engine and is utilized to provide most of the overall thrust, while an inner flow stream (known herein as a booster flow) passes through the fan, core engine, and turbine to provide power in which to drive the fan. In order to achieve an increase in fan pressure ratio and maintain fan efficiency with lower relative noise, the fan section includes two stages or rows of fan blades which rotate in opposite direction so as to be a counterrotatable fan. For lower noise and greater efficiency, it has become desirable to separate the two rows of fan blades axially to allow attenuation of the wake between them.
To reduce the extra length necessitated by the spacing of the fan blade rows, the inner and outer flow streams are separated at a location axially between such fan stages and the booster compressor positioned within the inner diameter of the second fan stage. Initial configurations of the booster compressor utilized in bypass turbofan engines included various stages of rotor blades which rotated in accordance with the first fan stage, as well as a stator vane stage positioned between each pair of rotor blades (see U.S. Pat. No. 6,220,012 to Hauser et al., for example). Thereafter, as seen in U.S. Pat. No. 4,860,537 to Taylor, U.S. Pat. No. 5,307,622 to Ciokajlo et al., and U.S. Pat. No. 4,790,133 to Stuart, the booster compressor was designed so as to have counterrotatable blade rows or sections therein which rotate in accordance with corresponding stages of the counterrotatable fan.
It has been found that driving the separate blade rows of the booster compressor introduces certain mechanical complexities. In addition, support for the second fan stage is required which does not unduly disrupt sealing of the outer and inner flow streams, particularly since the inner flow stream through the booster compressor must pass through the second fan stage. Thus, in light of the foregoing, it would be desirable for a counterrotatable fan section and counterrotatable booster compressor be developed which simplifies rotation of the second fan stage and the corresponding row of booster compressor blades. Moreover, it would be desirable for the second fan stage to be mounted and configured such that the inner flow stream through the booster compressor need not pass through the fan blades of the second fan stage.
In a first exemplary embodiment of the invention, a fan shaft assembly for a second stage of a counterrotatable fan section in a gas turbine engine having a counterrotatable booster compressor is disclosed as including a fan shaft extension connected to a drive shaft at a first end and connected to a disk retaining fan blades of the second fan section stage at a second end, a first platform member integral with the fan shaft extension at a first location so as to form a portion of an inner flowpath for the counterrotatable booster compressor, a second platform member integral with the fan shaft extension at a second location so as to form a portion of an outer flowpath for the counterrotatable booster compressor, and a plurality of compressor blades positioned between the first and second platform members, wherein the drive shaft causes the compressor blades and the second stage fan blades to rotate in the same direction.
In a second exemplary embodiment of the invention, a counterrotatable booster compressor assembly for a gas turbine engine having a counterrotatable fan section with a first fan blade row connected to a first drive shaft and a second fan blade row axially spaced from the first fan blade row and connected to a second drive shaft is disclosed. The counterrotatable booster compressor assembly includes a first compressor blade row connected to the first drive shaft, a fan shaft extension connected to the second drive shaft for driving the second fan blade row, and a plurality of compressor blades integral with the fan shaft extension so as to form a second compressor blade row interdigitated with the first compressor blade row, wherein the second drive shaft and the fan shaft extension cause the second compressor blade row and the second fan blade row to rotate in the same direction. The fan shaft extension further includes a first platform member integral therewith at a first location so as to form a portion of an inner flowpath for the counterrotatable booster compressor and a second platform member integral therewith at a second location so as to form a portion of an outer flowpath for the counterrotatable booster compressor, wherein each compressor blade is positioned between the first and second platform members.
In a third exemplary embodiment of the invention, a gas turbine engine is disclosed as including a high pressure section including a high pressure turbine, a low pressure turbine located aft of the high pressure section having counterrotating low pressure inner and outer rotors effective for rotating first and second drive shafts, a counterrotatable fan section completely forward of the high pressure section including a first fan blade row connected to the first drive shaft and a second fan blade row axially spaced from the first fan blade row and connected to the second drive shaft and a counterrotatable booster compressor including a first compressor blade row connected to the first drive shaft and a second compressor blade row interdigitated with the first compressor blade row and connected to the second drive shaft, whereby each low pressure turbine rotor respectively drives both a fan blade row and a compressor blade row. Each compressor blade of the second compressor blade row is integral with a fan shaft extension connecting the second drive shaft and the second fan blade row.